Oxidative stress is involved the pathophysiology of a large number of diseases. This stress originates not only from normal aerobic metabolism, but also from the metabolism of foreign compounds, and as a direct result of the release of reactive oxygen species by certain cell types. Organisms have evolved antioxidant defenses against oxidative insults, which include antioxidant enzymes and through the consumption of antioxidant compounds. A very important enzyme involved in antioxidant defense is glutamate-cysteine ligase (GCL), the rate limiting enzyme for the synthesis of the cellular antioxidant glutathione (GSH). The primary goal of this project will be to investigate the role of GCL in defense against substances and conditions which induce oxidative damage to the liver. We propose to characterize a transgenic mouse model of GCL overexpression, and to assess the effects of modulating GCL expression on susceptibility to oxidant-induced damage to the liver. We propose to use three agents known to cause oxidative liver injury, namely acetaminophen, carbon tetrachioride, and tumor necrosis factor-alpha. Transgenic and wild-type (normal) littermates will be exposed to non-lethal doses of these agents, and sacrificed from 6 to 48 hours later. Liver tissue will be excised and examined for signs of oxidative damage, cellular necrosis and apoptosis, and biochemical and cellular measures of cell viability and function will be made. Such information will be useful in determining the functional significance of GCL in defense against reactive oxygen species and xenobiotics which induce oxidative stress, and lead to a better understanding of the significance of variable GCL expression in humans.